The present invention relates to fiber optic cables and, more particularly, to fiber optic cables having a ripcord for ripping at least one cable component.
Fiber optic cables include optical fibers that transmit signals, for example, voice, video, and/or data information. Craftsmen require access to the optical fibers within the fiber optic cable, for example, for termination. Fiber optic cables designed for indoor, outdoor, or indoor/outdoor applications may include one or more ripcords to facilitate access to the optical fibers.
Ripcords rip cable components, for example, an armor tape of the fiber optic cable and/or the cable jacket, whereby the tear facilitates removal of the armor tape and/or the cable jacket for accessing buffer tubes having optical fibers therein. Conventional ripcords are threads or yarns made from dielectric materials such as nylon, aramid fiber, or polyester. The dielectric thread or yarn size of a conventional ripcord is generally specified by a denier. A denier is a unit of weight per length (grams per 9000 meters) of material for measuring the fineness of threads, yarns, and the like. Dielectric materials are used as conventional ripcords to make an all-dielectric fiber optic cable, thereby inhibiting damage caused by, for example, lightening strikes.
However, an all-dielectric fiber optic cable has disadvantages, for example, it is difficult to detect when buried. In order to overcome this difficulty in detection, a metal wire can be buried in close proximity to a buried all-dielectric fiber optic cable. Burying a metal wire with an all-dielectric cable for detecting the fiber optic cable is time-consuming, requires additional expense, and is burdensome.
To overcome burying a metal wire with an all-dielectric fiber optic cable, some fiber optic cables employ, for example, a corrugated metallic armor allowing the craftsman to detect the buried fiber optic cable. However, the corrugated metallic armor must be electrically grounded to inhibit damage caused by lightning strikes. Grounding the corrugated metallic armor of the fiber optic cable requires special hardware that clamps to the armor so that the fiber optic cable can be electrically connected to ground. Installing this special grounding hardware is also time-consuming, requires additional expense, and is burdensome. Moreover, fiber optic cables with different diameters can require different sizes of grounding hardware. Additionally, the corrugated metallic armor increases the outer diameter of the fiber optic cable, which is generally undesirable.
It is known that conventional ripcords can be located at various positions within a fiber optic cable. For example, U.S. Pat. No. 5,642,452 discloses a fiber optic cable with two conventional ripcords. A radially outermost conventional ripcord is located radially inwardly of strength members for ripping the strength members and an outer cable jacket. A radially innermost conventional ripcord is located radially inwardly of an inner jacket for ripping the inner jacket. U.S. Pat. No. 5,621,841 discloses a fiber optic cable having two conventional ripcords. The conventional ripcords are in diametrically opposed locations relative to a center of the cable, and the conventional ripcords are located radially inwardly of a steel tape and an outer sheath. The conventional ripcords are arranged for ripping the armor and possibly the outer sheath as well. U.S. Pat. No. 4,913,515 discloses a fiber optic cable with a conventional glass or aramid fiber ripcord located radially inwardly of optical fibers embedded in a plastic jacket. The conventional ripcord is operative to rip the plastic jacket, and the fiber optic cable may then be unrolled to define an optical fiber ribbon. U.S. Pat. No. 5,268,983 discloses a dielectric fiber optic cable with two conventional ripcords. A radially outermost nylon ripcord is located radially inwardly of an outer jacket for ripping the outer jacket. A radially innermost conventional ripcord is part of a core-tube jacket for ripping the core-tube jacket. U.S. Pat. No. 5,029,974 discloses a fiber optic cable with a conventional ripcord for ripping an armor tape and a cable sheath. U.S. Pat. No. 5,173,961 discloses a fiber optic cable with two conventional ripcords that lie partly within a metallic cable sheath and partly outside of the metallic cable sheath by extending between overlapping edges of the metallic sheath. The two conventional ripcords are applied in phase to avoid crossing of the conventional ripcords as they extend along the fiber optic cable. U.S. Pat. No. 5,321,788 discloses a fiber optic cable that includes a year or color marker under a tape, and includes two conventional ripcords for facilitating removal of an armor tape and a cable jacket.
Certain cable components, for example, a corrugated metal armor layer can require relatively high forces in order for the conventional ripcord to rip therethrough. Relatively high forces can cause conventional ripcords to break during the ripping action, which is undesirable.
Additionally, the craftsman can unintentionally sever the conventional ripcord when he is trying to expose and access the conventional ripcord. For example, when the craftsman is attempting a mid-span access he makes a ring cut around the entire circumference of the fiber optic cable in order to expose the conventional ripcord therein. A ring cut around the entire circumference is required because the craftsman does not know the circumferential position of the conventional ripcord within the fiber optic cable. During this ring cut the craftsman can unintentionally sever the conventional ripcord with his cutting tool. After the ring cut is made, the craftsman bends the fiber optic cable in an attempt to expose and access the conventional ripcord, however, in the process he may damage the fiber optic cable. Once the craftsman locates the conventional ripcord he passes a sharp extraction tool beneath the ripcord to withdraw it outwardly through the ring cut. However, this can be difficult and may require the craftsman to further make a longitudinal cut along the fiber optic cable to access a sufficient length of the conventional ripcord to permit use thereof.
One aspect of the present invention is directed to a fiber optic cable including a cable core having at least one optical fiber, a ripcord, the ripcord being an electrically conductive material operative, upon application of a sufficient pulling force, to rip at least one cable component for facilitating access to the at least one optical fiber.
Another aspect of the present invention is directed to a fiber optic cable including a cable core having at least one optical fiber, a ripcord, the ripcord having a portion being an electrically semi-conductive material operative, upon application of a sufficient pulling force, to rip at least one cable component for facilitating access to the at least one optical fiber.
A further aspect of the present invention is directed to a fiber optic cable including a cable core having at least one optical fiber, a ripcord, the ripcord having an excess length with respect to an associated portion of the fiber optic cable and being operative, upon application of a sufficient pulling force, to rip at least one cable component for facilitating access to the at least one optical fiber.